1. Field of the Invention
The present invention relates to an optical head for use in an information recording and reproducing apparatus for optically recording, reproducing or erasing information on a recording medium, such as an optical disk, an optical magnetic disk or the like.
2. Description of Prior Art
In this kind of information recording and reproducing apparatus, an optical head provided with a series of optical systems is used to record, reproduce or erase audio or visual information by using a light beam with high performance characteristics and operating to record, reproduce, or erase a random portion of the disk. For example, as shown in FIG. 1, the optical head is composed of optical elements, such as a semiconductor laser 1, a collimator lens 2, polarization beam splitters (PBSs) 3, 6 and 7, an objective lens 4, a condenser lens 5, a servo sensor 8, an RF sensor 9 and the like, which elements are mounted in a head block. Recently developed head blocks have been made light in order to shorten the seek time. In these head blocks, the optical head is divided into a fixed head unit 31 and a movable head unit 32 movable for seeking as shown in FIG. 2. In this case, the movable head unit 32 is provided with an objective lens 4 and a reflecting mirror 33. The objective lens 4 is supported by an unillustrated bobbin and is capable of being moved by an actuator (not shown) mounted at the movable head unit 32 in the focusing direction and in the tracking direction.
The fixed head unit 31 is provided with optical elements, such as a semiconductor laster 1, a collimator lens 2, polarization beam splitters 3, 6 and 7, a condenser lens 5, a servo sensor 8, an RF sensor 9 and so on.
An optical path L extends in a direction parallel with the seek direction between the fixed head unit 31 and the movable head unit 32, and optical path windows 31a and 32a corresponding to and positioned in the optical path L are disposed in the fixed head unit 31 and the movable head unit 32, respectively.
However, the conventional optical head having the above-mentioned composition has the following problems.
1. It is likely that dust, which intrudes into the blocks of the head units 31 and 32 through the optical path windows 31a and 32a, will stick and accumulate onto the face "b" of the polarization beam splitter 3 corresponding to the optical path window 31a and the face "a" of the reflecting mirror 33 mounted in the movable head unit 32 corresponding to the optical path window 32a. If the dust thus sticks and accumulates onto the polarization beam splitter 3 and the reflecting mirror 33, the effective value of the laser power is decreased, the light signal is influenced and the reliability of the servo signal is lowered.
2. Since the bobbin of the actuator for supporting the objective lens 4 is moved in the direction of the optical axis of the objective lens 4 in controlling the focusing direction, the objective lens 4 approaches and retreats from the optical head block (carriage) of the movable head unit 32. Therefore, when the objective lens 4 is far from the optical head block, dust is likely to intrude into the optical head block from above the reflecting mirror 33, and then stick and accumulate onto the reflecting mirror 33. If dust thus sticks and accumulates onto the reflecting mirror 33, the effective value of the laser power is decreased, the light signal is influenced, and the reliability of the servo signal is lowered.